Surface water hydrology is the sub-field of hydrology concerned with above earth water, in contrast to groundwater hydrology that deals with water below the surface of the earth. Its applications include rainfall and runoff, the routes that surface water takes (for example through rivers or reservoirs), and the occurrence of floods and droughts. Surface water hydrology is used to predict the effects of water constructions such as dams and canals. It considers the layout of the watershed, geology, soils, vegetation, nutrients, energy and wildlife. Modelled aspects include precipitation, the interception of rain water by vegetation or artificial structures, evaporation, the runoff function and the soil surface system itself. When surface water seeps into the ground above bedrock, it is categorized as groundwater, and the rate at which this occurs determines base flow needs for in stream flow, as well as subsurface water levels in wells. While groundwater is not part of surface-water hydrology, it must be taken into account for a full understanding of the behaviour of surface water.
In contrast to groundwater hydrology, which deals with water below the earth's surface, surface water hydrology is the area of hydrology that deals with water that is above the surface of the planet. Its uses include determining precipitation and runoff, the paths taken by surface water (such as through rivers or reservoirs), and the frequency of floods and droughts. The consequences of water engineering projects like dams and canals are predicted using surface water hydrology. It takes into account the watershed's topography as well as its geology, soils, plants, nutrients, energy, and wildlife. Factors that are modelled include precipitation, evaporation, the role of runoff, and the soil surface system itself. Other aspects include the capture of rainwater by vegetation or man made structures. Groundwater is defined as surface water that has soaked into the earth above bedrock; the pace at which this happens impacts base flow requirements for instream flow as well as subsurface water levels in wells. Although groundwater is not a component of surface water hydrology, it must be considered in order to fully comprehend how surface water behaves.